Recently, an LED comes into noteworthy display element, employed indoors and outdoors. With an increasing of a brightness of the LED, a demand for the LED has been increasing rapidly in display market, as an alternative device to neon lamp.
As an LED emits visible high-brightness light, an AlGaInP based DH-type LED has been known. FIG. 10 is a structural diagram of the AlGaInP based LED 100 (hereinafter, referred to as a first conventional embodiment) disclosed in JPB.H06-103759.
The LED 100 is manufactured by processing the following steps. As a first step, by using of MOCVD method, a n-AlGaInP clad layer 2 (thickness of 1.0 μm, Si-dope: 5×1017 cm−3), a (Al0.3Ga0.7)0.5In0.5 active layer 3 (thickness of 0.6 μm), a p-AlGaInP clad layer 4 (thickness of 0.7 μm, Zn dope: 5×1017 cm−3), a p-AlGaAs (electric) current diffusion layer 5 (thickness of 6.0 μm, Zn dope: 3×1018 cm−3) and a p-GaAs cap layer 6 (thickness of 0.02 μm, Zn dope: 1×1018 cm−3) are orderly grown on a n-GaAs substrate 1. And then, an electrode 9 is formed on the whole surface of the n-GaAs substrate 1, and an electrode 12 is formed on the p-GaAs cap layer 6. The outer region of a central circle portion of the p-GaAs cap layer 6 and the electrode 12 are removed by etching method.
The n-AlGaInP clad layer 2, the active layer 3 and the p-AlGaInP clad layer 4 of the LED 100 constitute the illumination part (or a light emitting part) 50. A PN junction is formed on the active layer 3. A bright light radiates from an electron—hole re-coupling phenomenon caused at the PN junction. When a (electric) current (20 mA) is supplied to the LED 100 covered by a cylindrical plastic package (diameter of 5 mm), the LED 100 luminous at 1.0 candela (described below 1.0 cd).
FIG. 11 is a structural diagram of AlGaInP based LED 200 (hereinafter, referred to as a second conventional embodiment) described in JPA.H04-229665.
The LED 200 is manufactured by processing the following steps. At a first step, by using of MOCVD method, an illumination part (or a light emitting part) which is composed of an n-AlGaInP clad layer 12 (thickness of 1.0 μm, Si dope: 5×1017 cm−3), a (Al0.3Ga0.7)0.5In0.5P active layer 13 (thickness of 0.6 μm) and a p-AlGaInP clad layer 14 (thickness of 0.7 μm, Zn dope: 5×1017 cm−3), are orderly grown on the n-GaAs substrate 11. As a second step, a p-GaInP cap layer 15 is formed on the layer 14. As a third step, a n-AlGaInP (electric) current inhibiting layer 16 (thickness of 0.3 μm, Si dope: 3×1018 cm−3) is formed on a center part of the layer 15, and then the outer region of a central circle portion of the layer 16 removed by etching method. As a fourth step, a p-AlGaAs (electric) current diffusion layer 17 (thickness of 6.0 μm, Zn dope: 3×1018 cm−3) and p-GaAs cap layer (i.e. contact layer) 18 (thickness of 0.02 μm, Zn dope: 1×1018 cm−3) are orderly grown on the p-GaInP cap layer 15 and the n-AlGaInP current inhibiting layer 16. As a fifth step, an electrode 21 is formed over all the n-GaAs substrate 11, and the other electrode 22 is formed on the layer 18. Then the outer region of a central circle portion both of the p-GaAs cap layer 18 and the electrode 22 are removed by etching method.
As explained above, the n-AlGaInP clad layer 12, the active layer 13, the p-AlGaInP clad layer 14 and the p-GaInP cap layer 15 constitute an illumination part (or the light emitting part) 60 of the LED 200. The light generated at the illumination part, is radiated from around the n-AlGaInP current inhibiting layer 16. Therefore, the amount of light reaching the underside of the electrode 22 is reduced, and the efficiency to take out the light from the body of the LED 200 is increased. That is, a total power of an out-leading light from the body of the LED 200 is increased, i.e., a brightness of the LED 200 is increased. When a (electric) current of 20 mA is supplied to the LED 200 molded in a cylindrical plastic package having a diameter of 5 mm, the brightness of the LED 200 is 1.8 cd.
Each of the LED 100 of the first conventional embodiment, and the LED 200 of the second conventional embodiment, has crystal defects called as hillocks which exist at a density of about 4,000 pieces/cm2. The hillocks reduce brightness because of absorbing the light and make an optical recognition of the electrode 12, 22 difficult so that it gives some trouble to its auto wire-bonding operation.